Applicable Systems
OBD-II Universal
Symptoms
The EVAP system leak detection pump has detected a leak. The code P0456 indicates a small leak (less than 0.040 inch) in the evaporative emission system.
Possible Causes
- Fuel cap loose, damaged, or not sealing correctly
- EVAP purge valve stuck open, allowing continuous flow
- EVAP vent valve stuck closed, preventing the system from sealing for the test
- Cracked or disconnected EVAP hose from the tank to the charcoal canister
Troubleshooting Steps
- Step 1: Check that the fuel cap clicks when tightened; inspect the cap seal for damage
Replace the fuel cap if the seal is cracked or distorted; clear the code and retest - Step 2: Perform a smoke test on the EVAP system to locate the leak
Inject smoke at the service port and look for smoke escaping - Step 3: Test the purge valve by commanding it open and closed with the scanner
Replace if it does not respond to commands - Step 4: Test the vent valve by commanding it closed during the smoke test
Replace if it does not seal
How to Reset
Reset: Clear the code after repair. The EVAP monitor runs on the next cold start and drive cycle.
Common Replacement Parts
- Fuel cap: OEM or EPA-compliant, match to vehicle (Always click 3+ times when tightening)
- Smoke machine: EVAP-compatible, low pressure (For leak detection)
- Purge valve: Solenoid, 12V, normally closed (Match to vehicle)
Frequently Asked Questions
- Q: What is the EVAP system?
Evaporative Emission Control system captures fuel vapors from the tank and routes them to the engine for combustion. It prevents fuel vapors from escaping to the atmosphere.
- Q: How common is a loose fuel cap?
It is the most common cause of EVAP codes. Always check the fuel cap first before more extensive diagnosis.
- Q: What is the EVAP monitor?
A self-test where the ECM seals the system and checks for pressure change. It runs on specific conditions: cold start, ambient temperature in range, fuel level between 15-85%.
Source: SAE J2012 Standard
Category: OBD-II